1. Field of the Invention
The invention relates in general to a multiplexing transmission system, and more particularly, to a smart different prime code multiplexing system
2. Description of the Related Art
To increase the capacity of an optical fiber communication system, conventionally, a time division multiplexing (TDM) is operated. However, due to the bandwidth limitation of the optical fiber, the wavelength division multiplexing (WDM) is more developed to replace the time division multiplexing. In the wavelength division multiplexing, a wave coupler is used to input each channel signal with various wavelength to each optical fiber. The receiver then outputs to each channel via an optical demultiplexer.
Lately, the technique of the conventional code division multiplexing access (CDMA) system has been widely discussed and studied. Using modifying prime code (referring to FIG. 1, the P7 and P3 modified prime code) as a decoding method, there are only P sets (P is the selected prime) of decoding capacity in the asynchronous code division multiple access (A/CDMA). In contrast, in the synchronous code division multiple access (S/CDMA) system, there are P2 sets of decoding capacity. However, the application of the division multiple access system to the optical fiber system decoder is still insufficient.
In the synchronous code division multiple access system, after spreading the codes of data, the synchronous state of each chip can distinguishes more prime codes. For example, using the P7 code as an example, there are only 7 codes (P7=7) can be distinguished in an asynchronous system. In contrast, there are 49 codes (p72=49) to be distinguished in the synchronous system. Providing a data transmission speed of 10 G/sec, the P7 code spreads the data transmission speed into a chip rate of 490 G/sce. It is a difficult task to achieve such an ultra high synchronous speed in an optical fiber.
In an asynchronous code division multiple access system, since the optical decoder does not contain any synchronous data, only P types of different prime codes are distinguished. That is, there are only P sets of decoding capacity that enables only P users to get access with an identical transmission channel.
In the above synchronous code division multiple access system, since the optical fiber contains synchronous data, P2 kinds of different prime codes are thus accessed. As a consequence, there are P2 sets of decoding capacity to enable P2 users to get access into an identical channel. In this manner, though the capacity is increased, a synchronous operation has to be achieved. The design to perform the synchronous operation is difficult and the hardware thereof is complex. For the design of the practical application in optical communication system decoder, the synchronous operation is even more difficult.
For example, in a conventional asynchronous system, while transmitting the spreading data by the asynchronous prim code, a technique of delay line in the decoder at the receiver is used to determine the threshold. Whenever the threshold is exceeded, the decoding operation is successfully fulfilled, and the required data are extracted. Referring to FIG. 2, in the synchronous system, a decoder of a receiving terminal 10 uses the technique of delay line 20 to determine the threshold 30. Meanwhile, a sampling time 40 synchronous to a transmitting terminal is set up. Only with certain sampling time 40, a determination whether the threshold 30 is exceeded is performed.
After prime code spreading of the data, the chip is greatly expanded (for example, with P7 code, one bit of data can be spread into 49 chips as shown in FIG. 3). The expansion is more obvious when the prime code is larger, especially for a high speed transmission, it is difficult to set up a sampling time to achieve a synchronous operation. This is the most challenge of the synchronous system.
The invention provides a smart different prime code multiplexing transmission system. Two different prime codes without interfering with each other are used and combined to replace the conventional asynchronous code division multiple access system. In the original optical fiber transmission system, additional users or data are dynamically added to improve the drawback of insufficient capacity of the prime code system, so as to increase the decoding capacity to achieve the objective of multiple access.
In the invention, a quasi synchronous parallel prime code is provided. By combining different prime codes, the asynchronous decoding capacity can be used, still in an asynchronous system, with a decoding capacity similar to that of a synchronous system. Moreover, an ultra-high capacity and an ultra-high operation speed are achieved.
In the method of operating the smart different prime code multiplexing transmission system, a prime code system is used. A monitoring system is assembled according to a first prime code system to select a second prime code system. When the monitoring system adds the second prime code system, the different prime code multiplexing transmission is operated according to the first prime code system and the second prime code system.
The smart different prime code multiplexing system provided by the invention comprises an optical decoder array, multiple opto-electronic converters, a channel occupied sensor, a slot occupied sensor, an overload decision device, an insert process unit, an insert control unit, and a different prime code decoder. The optical decoder array is used to extract a first prime code signal and to determine the operating status of multiple channels in an optical fiber. The opto-electronic converters are coupled to the optical decoder array to convert the optical signal of the operating status of the channels into an electronic signal. The channel occupied sensor are coupled to the opto-electronic converters to sense whether the channels are under the occupied or the empty states. The slot occupied sensor is coupled to the channel occupied sensor to reconstruct the first prime code signal in the optical fiber. The overload decision device is coupled to the channel occupied sensor to numerate the occupied channels. While the number of the occupied channels reaches a pre-determined value, a pre-determined signal is output. The insert process unit is coupled to the slot occupied sensor and the overload decision sensor. The insert process unit determines whether a second prime code signal can be inserted according to the first prime code signal and the predetermined signal. While it is permissible, an admitting signal is output thereby. The insert control unit is coupled to the insert process unit to receive the admitting signal. The admitting signal is then spread by the second prime code signal. The insert control unit is further coupled to the optical fiber. The different prime code decoder is coupled to the optical fiber to produce an output signal according to the second prime code signal.
A quasi synchronous code structure is also provided in the invention. The quasi synchronous code structure comprises different first prime code and second prime code. The coding method is between synchronous and asynchronous. The decoding capacity is similar to that of the synchronous system, while the structure can be applied to an asynchronous system.
The invention further provides a coding method. The data are coded into a second prime code using delay line technique. A data delay time with response to the second prime code is coded into a first prime code using delay line technique. The second prime code and the first prime code are coupled with each other by a coupler, so that a quasi synchronous code.
In another coding method of the invention, a first threshold and a second threshold are selected. After receiving a quasi synchronous code, the first and the second prime thresholds are input to individual decoded code using delay line technique, so as to decide whether the first threshold and the second threshold are exceeded. While individually coupling the first and the second thresholds, the phase shift of the thresholds is compensated. These two thresholds are coupled by a coupler and input to a threshold decision device. When the threshold decision device determines a signal, the received quasi synchronous code is converted into data to be output.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.